Digital Versatile Disc - Read Only Memory. Generally said of the disc itself, but also can be used the drive that reads is, differentiation is from writable DVD formats like DVD-R, DVD-RAM DVD+RW and DVD-R/W.
A typical DVD-ROM Disc is 5 1/4 inches in diameter, can be two-sided, with each side having two layers and each layer holding 4.3 gigabytes of data for an average total storage (excluding file system overhead) of about 17 gigabytes. Most DVDs use either the UDF file system or (less commonly) the ISO-9660/HighSierra file system.